Taking inventory of the county’s trees

Massive online map effort seeks help from residents

Robin Rivet, an urban forester-arborist at the Center for Sustainable Energy California, measures tree diameter. Her special measuring tape can calculate the diameter while measuring the circumference.
— Eduardo Contreras

Robin Rivet, an urban forester-arborist at the Center for Sustainable Energy California, measures tree diameter. Her special measuring tape can calculate the diameter while measuring the circumference.
— Eduardo Contreras

To paraphrase a poet, there may never be a poem as lovely as a tree. But, OK, just what is that lovely leafy thing worth, anyway?

An ambitious effort to map every urban tree in San Diego County aims to answer that question, quantify the value of all local trees and make a statement about a huge but often underappreciated resource.

“I really want to get the word out,” said Robin Rivet, urban forester for the California Center for Sustainable Energy, which is putting the map together. “The environmental benefits of trees are huge.”

The map, being assembled with help from the public, is evolving and available online. People will be able to find nearby examples of specific tree species; record varieties they see in their yards and elsewhere; use the site to identify trees they find; and get a calculation of monetary benefits, both individually and collectively.

On March 15, the map showed 296,504 trees with an estimated value of more than $4.8 million, but that’s only a small fraction of the county’s trees. The number should rise into the millions, and the value estimate will multiply. The database lists mostly municipally owned trees from 13 cities in the county. Only a few trees on private property, at businesses and in most parks have been inventoried.

The goal is to mobilize an army of “citizen scientists,” scouts, church groups, schools and landscape architecture students, to fill the gaps and provide a complete picture of the county’s urban canopy.

San Diego County’s numerous microclimates make it the “richest county in the nation for fruits and nuts,” Rivet said. “As a region, we can grow just about everything,” including tropicals and subtropicals.

The tree map, funded by a grant from Cal Fire, should make that diversity obvious.

“It’s a unique opportunity to share an observation of the urban forest as a whole,” said Mike Palat, chairman of the San Diego Regional Urban Forestry Council. “It’s going to create a great picture of the variety of trees, the condition of trees. It could be a tremendously useful resource.”

The website (sandiegotreemap.org) keeps a running tab of the trees’ “yearly eco impact.” The nearly 300,000 trees listed as of Thursday, according to the site, have reduced 19,622,883 pounds of CO2 from the atmosphere, conserved 83,213,745 gallons of water, conserved 8,502,988 kilowatts of energy, and reduced 46,244 pounds of pollutants from the air.

Kelaine Vargas, owner of a company called Urban Ecos, developed the program for San Francisco and is managing the San Diego County project. In San Francisco, there are dozens of agencies that manage the city’s trees, but before the map, there was never a complete picture, Vargas said. Besides helping demonstrate the trees’ value, the map has been a useful pest-management tool, she said.

People appreciate trees’ aesthetics, but recognizing their practical value tends to be more subconscious, Vargas said. If you’re walking on a sunny, hot day, you’ll find it much cooler in the shade of a big tree. But few people think about how much a well-placed, shade-producing tree can reduce air-conditioning costs. The map helps make that point.

That same big tree will catch rainwater in its canopy, hold more moisture in the soil with its roots, reduce runoff and soil erosion, and lessen the strain on a city’s storm drains.

The environmental and monetary benefits shown on the tree map site are calculated using software called i-Tree, which Vargas helped create with the U.S. Forest Service. Determining a tree’s ecological impact is based on three main variables: the species, the GPS coordinates and the diameter of the trunk.

Vargas said she has not encountered anyone who thinks the savings calculations are fuzzy, subjective numbers cooked up by a bunch of tree-huggers.

“There’s 10 years of research behind this,” she said. “People have respect for the scientific accuracy of the Forest Service.

“I’ve actually had people with the opposite reaction. They say by putting an economic value on trees, you’re diminishing the other values, like the spiritual, or the beauty.”

San Diego County is the fourth area and first multicity county to create a tree map. San Francisco was the first, followed by Sacramento and Philadelphia.

“A lot of businesses have concerns that trees block signage,” Rivet said. “But research shows that you’re much better off if you have trees outside your business. If you do, people tend to spend more time and money.”

Anyone can go onto the site and enter the species and location of a tree. (The site will be monitored for accuracy.) That could potentially raise privacy concerns, if someone were to, say, show a rare cherimoya tree in a neighbor’s backyard. But in this era of Google Earth and similar websites, people can already get overhead views of almost anyone’s property, Rivet said.

“We really weighed who would be using this map,” Rivet said. “I have 80 fruit trees, and I’m not concerned about it. The benefits far outweigh the risks.”

San Diego County lost an estimated 29 percent of its tree canopy in the 2003 fires and another huge chunk in the 2007 fires, although no survey has been conducted since. The recommended urban tree cover for cities in the West is 25 percent, Rivet said. San Diego’s cover has been estimated at 13 percent.